The drive towards higher density data storage on magnetic media has imposed a significant demand on the size and sensitivity of magnetic heads. This demand has been met, in part, by thin film inductive and magnetoresistive heads which can be fabricated in very small sizes by deposition and lithographic techniques similar to those used in the semiconductor industry. Thin film inductive heads are subject to the same problems as their core-and-winding predecessors of extreme sensitivity to gap irregularities and stray fields which result in output signal losses. Thin film magnetoresistive heads, on the other hand, rely on changes in the material's resistance in response to flux from the recording media and do not require precise gap modeling. For these reasons, inter alia, magnetoresistive elements are increasingly preferred over inductive heads for reading data stored at high densities on magnetic media.
A figure of merit for magnetoresistive (MR) elements is .DELTA.R/R, which is the percent change in resistance of the element as the magnetization changes from parallel to perpendicular to the direction of the current. Current magnetoresistance elements are made from permalloy (81% Ni/19% Fe), which, at room temperature has a .DELTA.R/R of about 3%. For improved response, a higher value of .DELTA.R/R is desirable.
Recently, it has been found that magnetic layered structures with anti-ferromagnetic couplings exhibit giant magnetoresistance (GMR) in which, in the presence of a magnetic field, .DELTA.R/R can be as high as 50%. The GMR phenomenon is derived from the reorientation of the single domain magnetic layers. For optimum properties, the thickness of the multilayers must be less than 3 nm, and .DELTA.R/R increases with the number of pairs of thin film layers. Thus, these multilayers provide significant challenges for production because of the precision with which the thicknesses and other features, such as interface roughness, must be maintained for the many iterations of the pairs of magnetic and non-magnetic films. Several studies have shown that GMR oscillates in magnitude as a function of the thickness of the non-magnetic layers, increasing the concern about thickness control. These layered structures are also subject to output noise from magnetic domains, and, since their outputs are nonlinear, the devices must be biased to obtain a linear output. Most reported work has been on Fe/Cr superlattices, however, Co/Cr, Co/Cu and Co/Ru superlattices have also been found to exhibit GMR.
The extreme sensitivity to layer thickness places significant limitations on practical and economical application of GMR to data. recording and other potential uses. It would be desirable to provide a method for forming GMR materials which is relatively insensitive to thickness and does not require multiple layers, and where the material is not subject to output noise caused by domains or to the nonlinearities of the layered structures. It is to such a method and material that the present invention is directed.